Electric control shaft



April 28, 1942. .1. c. RAH ET AL ELECTRIC ,CONTROL SHAFT Filed Dec. 4, 1940 .INVENTORS Jose/411 (I Ji'ah avflscar Hadley ATTOQNEY Patented Apr. 28, 1942 ELECTRIC CONTROL SHAFT Joseph C.'Rah, Indianapolis, and Oscar V. Hadlcy, Plainfield, Ind., assignors to P. R. Mallory & 00., Inc., Indianapolis, Ind.,"a corporation of Delaware Application December 4, 1940, Serial No. 368,436

3 Claims.

This invention relates to control shafts for electrical devices such as variable resistances for use in radio sets.

An: object of the invention is to improve re-v placeable and interchangeable shafts for elec .trical devices and the coupling means therefor.

Other objects of the invention will be apparent fromthe following d'escriptionyand accompanying drawing taken in connection with the appended claims.

In the drawing:

Figure l is a side view partly in section of a variable resistance device adapted to receive a. separable shaft, and a shaft adapted to be coupled therewith;

Figure 2 shows a shaft partially coupled to the variable resistance device;

Figure 3 shows the parts completely assembled; and

Figure 4 is a section onthe line 4-4. of Figure 3.

The present invention comprises an improvement in interchangeable shafts of the type shown and described in Marion J. Arvin Patent #2,l43,-

401, issued January 10, 1939. The improved shaft of the present invention comprises coupling means and means to provide a tight, well centered and easily assembled union.

Shafts of the type described are particularly well adapted for use in replacement volume controlsfor radio sets and the like. At the present timethe radio industry requires a variety of different types of volume control devices which may differ from each othernot only in the characteristics of the resistance element itself but also in the type or length of shaft to be used therewith. Heretofore, where volume controls have been manufactured with permanently attached shafts it has been necessary to manufacture each type of volume control unit with a variety of shaft types in order to suppl allthe requirements of the industry. With interchangeable shafts of the type contemplated herein it is only necessary to manufacture one style of volume control of each type and one style of interchangeable shaft of each length or type. The appropriate shaft can then be coupled with the desired volume control to produce any, assembly required.

However, in order to obtain all the advantages of apermanently attached shaft it is necessary that the interchangeable or replaceable shaft be capable of coupling with the volume control in such a manner as to produce a tight, well centered and easily assembled joint free from play and back lash.

While a preferred embodiment of the inventicn is described herein, it is contemplated that considerable variation may be made in the meth 0d of procedure and the construction of parts without departing from the spirit of the invention. In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring to the drawing the volume control element l0 comprises a case ll within whichare co-operating parts adapted to vary a circuit resistance in response to rotation of the control shaft. An insulating base I2 therefor carrying terminals l3 adapted to be attached to the appropriate parts of the radio circuit or the like is provided with a bushing I4 within which is a stub shaft 15 extending into the casing II for controlling the movable parts of the volume control. Stubshaft I5 extends out through bushing l4 and is restrained from movement into the bushing by a clinch ring l6 clinched within a groove inshaft l5 where it emerges from the bushing.

Shaft I5 is provided with a second clinch ring groove l! adjacent the groovecarrying clinch ring l6 outside the bushing. The part of shaft l5 extending beyond clinch ring I6 is likewise slotted crosswise with a slot l8 and is provided with a steppedaxial bore or socket comprising a larger portion 19 and a smaller portion 20 further in..

Shaft 2| adapted for assembly therewith comprises a cylindrical shaft portion 22 having extending across one end a milled fiat tongue-23 of substantially the same thickness as the width of slot la in stub shaft l5. Tongue 23 has slots 24 extending across opposite edges thereof, Projecting beyond tongue 23 is a post 25 of reduced diameter headed by a conical head 26, the largest diameter of which is slightly larger than post 25 so that a tiny flange 21 is formed by the edge of leader cone 26. The diameter of flange 21 is intermediate between the diameters of portions l9 and 20 of the socket in stub shaft l5. A base cone 28 joins the base of post 25 with the end of tongue 23, its larger diameter being slightly greater than the diameter of bore 19 of stub shaft [5.

The method of assembly of shaft 2| and volume control element In is as follows, reference being had to Figures 2, 3, and 4 of the drawing.

Leader cone 26 of shaft 2| is first inserted into larger diameter bore IQ of the socket in stub shaft 15, which can readily be done since the outer diameter of flange 21 is slightly less than the diameter of bore [9. The shaft is allowed to slide in until tongue portion 23 enters slot I8 in the stub shaft thereby aligning the tongue and the slot. This brings leader cone 26 to the beginning of small diameter bore 20 of the stub shaft.

Assembly is then completed by pressing shaft 22 into place with a manual pressure or it may be set into place by gently tapping it. Leader cone 26 enters small diameter bore 20 and tiny flange 21 is furled back or sized over as indicated in Figure 3 allowing the cone to enter small bore 20 with a tight well centered fit free from play. Base cone 28 enters large diameter bore 19 with its larger base jamming the end of bore I9 therebyproviding a tight fit at this point. This also brings slots 24 in tongue 23 into registry with groove I! in stub shaft l5, the shafts thereby producing a complete circumferential groove. A clinch ring as is then inserted in the groove thus produced and clinched to lock the shaft sections together thus completing the assembly. It will be noted that the invention permits alignment of tongue 23 with slot l8 prior to final setting of the shaft permanently in position.

The spacing between flange 21 and the large base of cone 28 is great enough to prevent any substantial rocking of the shaft after it is set in place as described.

Should the operator, by accident, select the improper shaft for the desired application and complete the assembly, the shafts may be again disassembled by opening clinch ring 30 and withdrawing shaft 22 from the socket. Shaft 22 may be readily reprepared for tight assembly with another volume control unit by simply raising flange 21 with a pen knife or other object so that it will again provide a tight fit.

It will be obvious that the present invention results'in a replaceable, attachable, detachable, interchangeable control shaft for volume controls, variable resistances and other types of devices, wherein the shaft coupling is required to be tight, well centered, free from play or backlash, and easily assembled and disassembled.

'While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to'cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. A'control shaft coupling for adjustable electrical devices comprising a pair of shaft sections having interlocking portions for connecting them together end to end, said portions comprising non-circular interfitting parts fitting together to form a substantially circular joint, said interfitting parts being correspondingly grooved to provide a circumferential groove in said joint, and a clinch ring in said groove locking said sections together, the first of said sections having a central bore extending back from said joint, said bore having a, larger diameter outer portion and a smaller diameter inner portion, and the second of said sections having a post extending into said bore, and a flange near the end of said post intermediate in size between said smaller and larger diameter bore portions, said post being longer than said larger diameter bore portion and shorter than the combined length of said portion and said shaft joint to permit alignment of said interlocking portions prior to entry of said flange into said smaller diameter bore portion.

2. A control shaft coupling for adjustable electrical devices comprising a pair of shaft sections having interlocking portions for connecting them together end to end, said portions comprising non-circular interfitting parts fitting together to form a substantially circular joint, one of said sections having a central bore extending back from said joint and the other of said sections having a post extending into said bore, said bore having a smaller diameter inner portion and a larger diameter outer portion, said post terminating in a conical end of larger diameter than said post, the flange thereby provided by the edge of said conical end being intermediate insize between said smaller and larger diameter bore portions, said post being longer than said larger diameter bore portion and shorter than the combined length of said portion and said shaft joint to permit alignment of said interlocking portions prior to entry of said flange into said smaller diameter bore portion.

3. A control shaft coupling for adjustable electrical devices comprising a pair of shafts having interfitting portions for keying them together end to end, and means for aligning said shafts and preventing loose play therebetween comprising a longitudinal bore extending inward from the end of one of said shafts, said bore having a larger diameter outer portion and a smaller diameter inner portion, and a longitudinal post on the end of the other of said shafts, and a fiange on the end of said post having a diameter intermediate the diameters of the larger and smaller ends of said bore, whereby said post may be first inserted part way into said bore to align the interfitting portions of said shafts and then pressed further into said bore to bring said interfitting portions into final keyed relation and to bring said flange into firm engagement with said smaller diameter inner portion of said bore to produce a, tight fit.

JOSEPH C. RAH. OSCAR V. HADLEY. 

